01 Feb Biopsy Techniques used for PGD in ART labs
Most clinics perform a cleave-stage embryo biopsy. However, one of the following 3 techniques can be used for pre-implantation genetic diagnosis (PGD).
Polar Body Biopsy
Polar Body Biopsy is done for chromosomal disorders in females only. The mature metaphase II egg expels a single polar body, which is removed for testing. It provides information on only the chromosomal content of the egg. Most importantly, this provides information about the chromosomal composition of the future embryo.
Cleavage-Stage Embryo Biopsy
In PGD/PGS, cleavage-stage embryo biopsy is done to biopsy a single blastomere. This allows extraction of a single blastomere from a developing embryo. The removal of the blastomere is quite challenging. The objective of an embryologist is to remove the cell with lowest trauma to the remaining embryo. Before extracting a single cell from a 6-10 cell embryo, the embryo is matured in a medium for around 20 minutes in order to reduce blastomere-to-blastomere adherence.
The embryo is held from one side using a holding pipette and a small opening is made inside the zona pellucida to reach the blastomeres. This is called assisted hatching. It is performed using a dilute acidic Tyrode solution or a laser, in some cases, using a sharp curette. Once the opening is made, a pipette is moved across the opening and targeted on the chosen blastomeres. The blastomere is extracted in a pipette and released into the present medium.
The embryo with one lesser blastomere is transferred back to the suitable culture followed by processing of the blastomere for FSH or PCR depending upon the genetic condition that needs evaluation.
Blastocyst formation cycle starts from 5th day of egg retrieval. At this point, the embryo is formed at more than 100 cells. A hole is breached in the zona pellucida and cells are removed from the trophectoderm. Genetic analysis is performed using FISH or PCR analysis.
Genetic testing is completed within 24-48 hours of the embryo biopsy and many of the embryos don’t survive until the time of embryo transfer. However, the biopsied blastocyst must be frozen.
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